Phase and amplitude perturbations observed on subionospheric VLF signal recorded at Varanasi (L = 1.07) using SoftPAL Receiver

We report here preliminary observations of phase and amplitude perturbations in VLF signal propagating in the Earth-ionosphere waveguide, monitored at low latitude station Varanasi using SoftPAL Receiver. Phase and amplitude perturbations (trimpis) on VLF signals consists of a sudden change in phase and amplitude of the transmitter signal followed by a slow recovery to the initial levels as the ionization decays. The current understanding of lightening discharge associated processes that leads to the changes in the characteristic of the waveguide and thus variation in the received amplitude and/or phase of the VLF transmission signals have been reported.